Mini-Keels vs Boards - Opinions ?

[Randy]

Originally Posted by eyschulman

a loaded multi will not do well board or not-think trade winds and down wind sailing in multi-The main advantaes of the multi are at anchor shallow draft -wide cockpit-and the light and airy upper deck and salon areas.When it comes to passage performance up or down wind I believe the modern(not old tech compare apples to apples)) mono has a significant edge-there are now many monos designed for ocean passages and live aboard that can do the 200 mile day. Down wind with modern sails and handeling gear these boats can surf along in the teens with good safe contol short handed. up wind the multi cruiser(ususally overloaded) is a piggy compared to these modern monos. The reason multis can thrash monos in races is a mater of weight,weted surface and sail carring ability and none of these advantages of racing multis are pertanent to the average loaded liveaboard housamaran. Your choice I believe comes down to style and what appeals to your honey.

You're nuts!!

[thinwater]

Originally Posted by Randy

You're nuts!!

It counts. She's my best mate... so to speak.

My view? I've owned a chute equipped beach cat, a Stiletto, and now a PDQ. I loved them all, for different reasons.

[Stein]

This topic is of course one that has no final answer. But reading the above posts gives me some thoughts. Well, a lot actually, but that’s normal, (for me anyway, although the thoughts probably aren't). I’ll try to restrain myself, but probably will not succeed.

Firstly, it seems like you have decided that the boat you want is a cat. I think that's a good decision. One reason is that I'm a multihull fanatic. The other is quality of life while living aboard, at anchor or, more importantly, when sailing off shore upwind. You’ve probably discovered it already, but cats are MUCH more comfortable going upwind in a blow, and also quite a bit faster than similar monos, no matter which type of keel. And make no mistake: A sailboat that you cannot, or in real life will not endure sailing upwind, is in my book no sailboat. It's a pathetic camper. Sorry. The fanatic in me is talking. But also it's a dangerous contraption. Some time on a long trip one will be in relatively strong winds on a lee shore. In proper ocean waves, motoring just doesn't work. If not able to go to windward to some little extent, you're in trouble.

No cruiser, not even the really fast ones, will give any noticeable feeling of playful sailing, like the stuff a beach cat will throw at you in bucketfuls. Cruisers are too big so you lose the agility and closeness to the sea, and they are way too heavily laden, even if you are very restrictive, to perform near their best. Even the most extreme pro racing multihulls are not actually fun to sail. They’re wildly impressive and exiting, but not really fun. They feel like proper ships. (Let alone the similar monos!) If you want sailing fun while cruising, bring a toy, like a beach cat, sailboard or kite and board. Nothing beats them in the fun arena.

You mention a 44 foot size. For two, that is a big boat.... It's clearly not too big, but big enough to make everything a bit harder to manage. Holding the boat by hand while arriving at or leaving a pier will be close to impossible if there is a bit of wind. The sails are too heavy for one or maybe even two persons to lift from the ground. Even nicely wrapped and put in a bag, you may need a crane. The anchor and chain is big stuff. Pulling it by hand is not possible, even with no wind. If you choose daggerboards, they need winches to be lifted. Maintaining it is much more expensive than with a smaller boat. Also entering ports in colourful places, a big cat will label you as millionaires and make it hard to get close to the locals, apart from the ones you don’t want close. A 35ish boat could reverse most of those problems. It also lacks a lot of space and comfort and is more jumpy in a seaway, so a conscious choice must be made...

On the daggerboard versus fixed skeg / short keel discussion, much has been said already, but I'll have a go at it too: The performance difference between the two types is more related to the total package than it is to that single feature. Cats with daggers tend to have more sail, more efficient sail plan, less weight, better hull shapes, etc. Daggers are of course also deeper and it's easier to make an effective wing shape, so that alone will contribute significantly, but on two otherwise exactly equal boats, the overall performance difference isn't overwhelming. I'm very performance oriented, so I'll always choose daggers, but you call this your "retirement boat". I think that points towards easy handling and fewer worries. Go for a boat that is a serious sailboat, but one that has fixed keels.

Also mentioned in this thread is capsize. A cat with long daggers fully down will definitely be more vulnerable to gusts etc than a similar fixed short keel cat. But the reason is not what many believe it to be. There is no way I can avoid going a bit nerdy if to explain this properly, but it's not really complicated at all. To start bluntly: I’ve seen claims that cats with skegs can “slide” sideways at a speed of several knots. This is not reality. Even given ideal conditions, with no previous forward motion, no cat can move sideways at a speed that would make a difference when regarding capsize (unless the water also moves with it, like on a breaking wave). A wide and flat dinghy like the Laser, with keel and rudder off, could be towed sideways at a couple of knots or maybe three. A cat with its relatively narrow hulls, and two of them, will create such an enormous amount of turbulence that it will not happen. The reason for difference in capsize properties is not at all related to this.

If we consider two equal cats with different keel solutions, both develop exactly the same leeward acting side forces in the rig. Those are by the laws of physics bound to be countered by the exact same amount of opposite windward acting side force generated by the hulls and appendages. This equilibrium is constantly varying, but always will balance. The shorter fixed keel generates this side force at a greater glide angle (leeway) than the dagger, and thus also generates more drag (resistance to forward motion), so it will be a bit slower and not move quite as high towards the wind. The heeling forces are exactly the same, BUT the heeling moment is significantly different, the leverage arm. Not in the rig, as they are equal, but the centre of effort of the underwater area (lateral area) is quite a lot deeper down.

Say the short keel is one meter / 3 feet and the dagger is double (a larger difference is normal). The not too efficient shape and the insufficient area and aspect ratio will make the short keel increase the drift angle until it gets enough to counter the rig. At this drift angle, even the hull itself will contribute, like on a Hobie 16, (but this gives a high drag penalty). The centre of effort (CE) would be at maybe 0.3 meters / one foot below the surface. On the other equal boat, the generation of side force is totally dominated by the highly efficient dagger, which is protruding much deeper than the short keel. We may expect to find the CE at 1 meter / 3 feet below the surface. The CE is kind of where the "pulling wire" is attached. Moving it to three times deeper is nowhere near tripling the tendency to capsize, but it's still a definitive difference. Same thing as moving the whole rig a bit higher up in the air, but not changing anything else.

Pulling up the daggers to same depth as the fixed keel may still leave the CE deeper due to better wing shape. Pulling it all up, will move CE higher than on the fixed keel boat, but not too much, as CE on the fixed keel version as mentioned already is much affected by the hull. To repeat the conclusions: Position of the CE is the only real reason for higher tendency of capsize with a daggerboard cat. Likewise: Fixed keel boats do not get any noticeable bonus by sliding sideways when being overpowered. They resist sideways movement exactly as hard as any equally rigged boat. The only help they get is that the higher glide angle (leeway) and slightly lower speed will give a miniscule reduction in apparent wind. But in strong wind when capsize is possible, the smaller keel is closer to sufficient (foil lift increases roughly proportionately to the square of the speed increase, as long as laminar flow is kept) and the difference in windward performance should be insignificant or none if all other features are the same, which they rarely are.

Stein

[sandy daugherty]

Boards stall, leaving a daggerboard equipped boat free to slip sideways.

Minikeels continue to offer "barn-door" lift even when the boat has little forward motion.

This distinction is quite obvious. A minikeel sailor at the helm of a daggerboard boat must learn to keep the boards flying, or he will slide down wind to an embarrasing degree.

If the boat is moving fast enough for the boards to develop lift, it has steerage and can be controlled. It can turn faster than the minikeeled boat.

If two similar cats are placed beam to on a breaking wave, the board boat will be able to correct its heading faster if there is way on, but will offer less lift if not. The minikeeled boat is more likely to trip. However:

The entire discussion is moot; as Richard Woods has pointed out, the wave has come and gone faster than we are allowing, and neither boat has advantage. Both will likely survive, upright or inverted, while a full keeled, heavily ballasted monohull will assume a kindly angle, on the bottom.

[emcmia]

Have a 43ft Privilege (extended to 48ft) with 18" by 12 ft long keels; draft 4ft. Hull material is kevlar bi-axial composite. Have been sailing it since 1995 (after owning 45ft CC Freedom sloop and 41ft Morgan OI415 sloop). 2 years ago, I hit an uncharted reef in the Bahamas, while motoring at 9+ knots. Other than taking a fist sized chunck out of the starboard keel and a slightly bent rudder shaft, no other damage. My opinion: if you're a "purist" trying to eke out the maxium speed under conditions suitable for your cat, daggerboards are probably the way to go. If safety is an issue, I am obviously biased to the fixed keels. When I am hauled or even on a sandbar at low tide, the boat rests level on the keels.

As for pointing, about 40 deg with true wind less than 15kts. However, let it pick up to 25kts and I can get close to 30 deg. My max speed under sail to date is just under 15kts, beam reach with 20-25kts apparent. 10 to 12kt is not unusual. (Last time hauled, the weight was measured at 30k lbs.)

As for range, we routinely motor on a single engine at 7.5 knots, which extends our range to more than 700 miles (120 gal fuel capacity without spare containers).

Good luck on your selection.

[Stein]

Sandy.
I didn't explain my point clearly. I’m sorry. I’ll try to elaborate it better. You are of course right. If the forward speed is too low for the actual side forces, like just after a tack with tight sails, the leeway may be too much and give an angle of attack that makes daggers stall (which angle depends strongly on their shape). This is the same effect as with a glider plane. When the speed is too low, it will drop like a leaf (but regaining lift is not too hard.) Daggers are high aspect ratio foils. Their ability to regain laminar flow (actual foil function) is inferior to the fixed skeg type lateral plan, which has a very low aspect ratio. The latter normally have much larger profile area and, as you describe, a "barn door" type ability to give a useful leeway resistance even when stalled. Stalled daggers also produce a strong vortex that is resisting normal speed and counteracting buildup of laminar flow. The conclusion is that a daggerboard boat may easier end up "in irons" if you lose much speed in a tack and do not compensate by releasing sails a bit (less sideways force).

But another conclusion is that if the boat speed is too low, a daggerboard cat will “slide” sideways more easily than a skeg keel cat. But in the context of capsize risk, this will not help the daggerboard cat at all, as its CE is still quite much further down than its equal with a skeg. The sideways “sliding” speed of either will anyway never exceed numbers that are totally insignificant when seen in context with the wind speed capable of making a capsize situation. The (very slight) difference in ability to “slide” sideways, either stalled or not, may have significance in other situations. One would be when the boat is broadside slammed by a wave. Here the relative speeds and masses are totally different from the wind equivalent. Ability to “slide” a bit will soften the blow noticeably.

So far, I have assumed that the two layouts have identical hulls, apart from the keel profile. In real life, cats with skeg keels tend to be heavier with more V shaped hulls sitting deep in the water. At least modern daggerboard cats have quite rounded profiles, and tend to me more racy and light, meaning that they sit more “on top of” the surface. Lifting the daggers will of course then make the daggerboard cat able to “slide” much more than its differently shaped skeg counterpart. Still, the “slide” will not affect capsize forces to any meaningful degree. The changed heeling moment by removing the deep CE (daggers) on the other hand, will be clearly noticeable.

I will always prefer a daggerboard cat. That’s because my style of sailing is the actively participating type. At no time will my main sheet and steering be left more than one second away. I will have a lot more sail up than most. I like that. I like speed. Most cruisers are different and may quite often be better off with skeg type boats. Daggerboard cats do demand more attention, or they become a greater risk. That’s a non debatable fact. But they can to a slight effect be used to increase safety in some situations too. Like when being banged about in rough seas with little control, they are somewhat less prone to trip over their own hull from pure wave action. A bit more like a cork. But that effect should not really affect which type of keel layout you choose.

I hope this was more precise. I know it’s nerdy, but it can’t be helped I think. Or maybe it could if I mastered the English language better.

Stein

PS
Emcmia. I'd also like to repeat what you experience with your cat. Fixed keel cats behave noticeably inferior to daggerboard cats in light winds when only considering speed and upwind VMG. But with normal good sailing conditions, say 10 knots wind or more the difference is only interesting in competitive context. In really strong wind there is hardly a difference at all.

[44'cruisingcat]

In any conditions where capsize was even a remote possibility you wouldn't have a daggerboard fully down. You'd have it fully raised.

[dwightsusan]

I'm a bit confused in some of the technical discussion in this thread. Probably a combination by my passion for performance and my reliance on intuition rather than science.
I have a hard time understanding why a retractable dagger board multi should be any more, or less, likely to capsize than one with a "mini-keel". First, capsize has become exceedingly rare as multihull design has improved, to the point of being mostly of historical interest. Second, the biggest risk seems to me to be one of pitchpoling (maybe a bit diagonally) at the bottom of a steep wave as the leeward bow buries in the back of the next wave, something related mostly to boat speed, sea conditions, and forward hull design, but not to daggerboard/mini-keel issues. Getting caught beam to in a large breaking wave, whether you slide down the wave face with inadequate lateral resistance or you "trip" over your retractable or fixed appendage, is going to put you equally in harms way as the wave breaks over you, albeit more so in a smaller multi with a narrower beam. Going over to leeward when beating or reaching in high wind seems something for the racer flying a hull to consider and probably has nothing to do with what's hanging from the bottom of the immersed hull.
Bottom line for me: Deploy an amount of sail appropriate to existing and anticipated conditions, never get caught beam to in large breaking seas, control speed by shortening sail early (and extending daggerboards, if present), and then deploying a drogue when the sh.. really hits the fan. Although probably excessive, we have a quick release handle incorporated in our mainsheet tackle, which I always reach for whenever wind and speed start to lift one of our light narrow hulls, so far a handle I have never pulled.
I don't get the concept that an underwater appendage generates "lift" to windward. Water is not air. I believe lift produced by laminar flow over a sail is a product of pressure differential between the "thinned" fast moving air to leeward (low pressure) and the "compressed" slower moving air to windward (high pressure). Water is not compressible and therefore resists any disturbance. Laminar flow over a moving appendage is optimal as it represents the least possible disturbance of the water. This seems to me to be the force limiting leeway when beating or reaching, and seems to me to be dependent mostly on lateral area and shape of the appendage. I believe asymetrical fins (or hulls) are no longer in vogue as they break up laminar flow of non-compressible water, adding drag while generating no lift whatsoever. I can't fit the concept of stalls (what happens to a wing when lift becomes less than the weight of the aircraft) into my understanding of underwater appendages. Sails can stall when "lift" produced by sails decreases below the resistance of the water to the forward motion of the boat, then forward boat speed bleeds off. When underwater appendages lose laminar flow, the boat is slowing to a stop as it gets pushed to leeward with the appendage presenting only the resistance relative to its lateral area. It seems intuitive to me that laminar flow over a relatively fine high aspect ratio fin disturbs water less, and is therefore faster.
Bottom line for a self confessed speed freak like me: I need the speed and flexibility I get from my twin, relatively fine, high aspect daggerboards, which I can control anywhere from fully extended (almost eliminating leeway, and maybe slowing the boat a bit in very high winds) to fully retracted (allowing the long narrow half round hull section with nothing - no fin, no prop, no skeg - but a bit of likewise retractable rudder to minimize wetted surface and friction drag). And I can run or moor in 15" of water, an immense advantage.
But, hey, it's all sailing. A lateen rigged little punt, a 45 knot speed trials multi, a Chinese rigged junk, an offshore racer, a windsurfer, an ancient square rigger, a roomaran, my performace cat - the worst day offshore on any of these beats the he.. out of the best day on the beach.

[svstrider]

My Malcolm Tennant designed 47 ft cat has dagger boards AND mini keels. I have never seen that before on a cat. Has anyone else?

I am not sure whether that gives me all the disadvantages and none of the advantages of either or a little bit of everything (good and Bad).

Pelican sails to windward better than any other cat I have been on. She draws 0.8 meters with boards up and 2.5 metres with boards all the way down. Should I be scared or delighted??

[smj]

Originally Posted by svstrider

My Malcolm Tennant designed 47 ft cat has dagger boards AND mini keels. I have never seen that before on a cat. Has anyone else?

I am not sure whether that gives me all the disadvantages and none of the advantages of either or a little bit of everything (good and Bad).

Pelican sails to windward better than any other cat I have been on. She draws 0.8 meters with boards up and 2.5 metres with boards all the way down. Should I be scared or delighted??

The Maine Cat 30 has a single daggerboard and mini keels. Not sure about the 41.

[svstrider]

Originally Posted by smj

The Maine Cat 30 has a single daggerboard and mini keels. Not sure about the 41.

I was just reading Chris Whites FAQ re his Atlantic cats Atlantic Catamaran FAQ - by Chris White Designs
They also have both minikeels & dagger boards for beaching and prop / rudder protection. So my cat is not TOO unusual.

[clockwork orange]

I used to own a Macgregor 36 cat with a single daggerboard in the port hull which worked well,i think the only reasons for having two is redundancy and mans desire for symmetry,i talked to a guy who ran two Mac 36s as day charter boats,a 1979 with a single board and a 1981 with two boards and he claimed the single board boat tacked better and gave away nothing upwind. It seems to me if you are of the type who does your own maintainance a mini keel cat would allow access to more of the bottom of the hulls for cleaning and painting while sitting on a sand bar than a board boat which has a large part of its belly inacessable.
Steve.

[neelie]

Originally Posted by 44'cruisingcat

I'm not saying mini-keels don't have advantages - they do. Like everything there are pro's and cons to both.

Phew at last!... could have saved 3 pages of angst, if someone had said this in post #2..

[nautical62]

Having owned a centerboard trimaran I have to say I'm not a big fan of center/dagger boards on cruising boats.

I do like they give performance that can be pulled up for thin water.

However, I'm a big fan of the KISS principle and I think they add a lot of potential for problems. Potential leaking for one. Also, if you damage one, they be very hard to remove and install and I feel the housing greatly increases the odds of having hull damage. Since catamarans are fairly shallow draft anyways, I just don't see the positives outweighing these negatives.

I think everyone needs to consider their own priorities, but those are mine.

[Canibul]

Interesting you lump daggerboards and centerboards together. They are really not the same thing at all, are they. Its also interesting to see monohull owners talking about catamarans. Kind of like getting your Chevy review written by a Ford fanatic....

After following so much of this for so long, I have finally learned that if I want good information on a catamaran, I need to be talking to someone who is sailing a catamaran. And I mean that. NOT someone who once sailed a catamaran. Or who had a friend who knew a guy who sailed a catamaran. Because today's catamarans are not the catamarans someone was once sailing.

Look at the numbers. Who moves from a monohull to a multihull? LOTS of people. Who moves from a multihull to a mono? Not many. Very very few, in fact.

Kick up centerboards are not the same as daggerboards. Low aspect keels are not the same thing as other keels. Monohull sailors are basically good for talking bout monohulls. People who think 5 or 6 ft. means shallow draft are not the people to be talking to about shallow draft.